References are cited herein to indicate state of the art and are not to be taken as acknowledgement of specific relevance to patentability of the invention.
Bibliographic details of the publications referred to by author are provided at the end of the specification.
Crop losses due to infection by fungal pathogens are a major problem in the agricultural industry and each year, millions of dollars are spent on the application of fungicides to curb these losses (Oerke, 2003). Nature is a rich source of antimicrobial peptides, many of which exhibit antifungal activity.
Antimicrobial peptides that have evolved to protect organisms from pathogens. Their specificity appears to depend largely on the organism from which they originate, probably due to evolutionary pressure placed on these organisms by various pathogens. As such, peptides isolated from mammalian species generally exhibit a higher degree of activity toward bacterial pathogens compared to fungal pathogens, presumably due to the higher risk of infection from bacteria. In contrast, plant antimicrobial peptides generally display higher antifungal activity due to the higher risk of fungal infection faced by plants.
Plant defensins represent one class of antimicrobial peptide (reviewed by Lay and Anderson (2005)). There is a wide variety of defensins with differing spatial and temporal patterns of expression and spectra of activity. These include RsAFP1 and RsAFP2 from radish, Ah-AMP4 from Aesculus hippocatanum, and AlfAFP from alfalfa, pI39 and pI230 from pea, and DmAMP1 from dahlia as well as ZmESR6, PhD2, PhD1, BSD1, RsAFP4, WT1, RsFP3, AhAMP1, CtAMP1, HsAFP1, HvAMP1, PsD1, AX2, AX1, SoD2, VaD1, gD1, NaD2, J1-2, SD2 and EGAD1, and preferably floral defensins such as NaD1 and NaD4 from Nicotiana alata and Tomdef2 and Tomdef3 from Lycopersicum cerasiforme. 
The mechanisms underlying the specificity of these peptides remain unknown, although interactions with the cell surface are presumed to be involved. Since membrane permeabilization is a common activity of many antimicrobial peptides and the membrane composition of various cell types is highly variable, the presence of specific lipids is postulated in some cases to be responsible for peptide susceptibility. In particular, the plasma membrane of bacterial cells contains negatively charged phospholipids in the outer layer while mammalian cells do not (Matsuzaki, 1999). These negatively charged lipids could interact with positively charged antimicrobial peptides. In support of this hypothesis, in vitro studies have demonstrated that the presence of negatively charged lipids is important for the membrane permeabilizing activity of a number of antimicrobial peptides (Matsuzaki et al, 1995; Matsuzaki, 1999; Ladokhin and White, 2001; Epand et al, 2006).
Membrane permeabilization has been suggested as a mechanism for some plant defensins, although the mechanism of permeabilization has not been investigated. In the case of the plant defensins RsAFP2 and DmAMP1, permeabilization is proposed to involve a specific receptor on the cell surface. The presence of specific sphingolipids in the plasma membrane is also required for the activity of these defensins, possibly as binding sites (Thevissen et al, 2000a, b; Thevissen et al, 2004; Thevissen et al, 2005, Ramamoorthy et al, 2007).
Chemical fungicides are quite commonly used in agricultural and horticultural settings. Strobilurins and triazoles are particularly important for use in these industries.
Strobilurins include strobilurins A through H, azoxystrobin, kresoxim-methyl, picoxystrobin, fluoxastrobin, oryzastrobin, dimoxystrobin, pyraclostrobin, metominostrobin, and trifloxystrobin. For a review of the fungicidal strobilurins, see Bartlett et al (2002). As a class, the strobilurins are part of the Q01 (Quinone outside inhibitors) cross-resistance group, and they inhibit sensitive organisms by binding cytochrome b and inhibiting electron transport and ATP synthesis.
The triazole fungicides are characterized as demethylase inhibitors, and they interfere with sterol synthesis in sensitive fungi. Triazole fungicides are described in U.S. Pat. No. 4,767,777, for example.
There is a need in the art for improved economies of agricultural production and improvement of crop yields. Fungal disease is a significant source of yield loss and current strategies for fungus control are both expensive and potentially damaging to the environment. There is a need for new systems for protecting agronomic and ornamental plants from disease, especially fungal disease. Disclosed herein is a system for reducing economic loss resulting from damage to crops and ornamental plants caused by pathogenic agents, such as fungal agents. In addition to significantly reducing plant damage, the cost of production can be reduced by decreased use of chemical pesticides.